How to check if an object exists within another object using JS

Question

Suppose i have an array of objects

var arr= [{name:'John', lastName:'Smith', age:25}, {name:'Steve', lastName:'Johnson', age:56}];
var obj1 ={name:'John', lastName:'Smith'};

How to check if an object exists within another object using JS ?

Will nested looping do the trick ? The first loops through the objects inside the array, the second loops through key/value pairs inside the object and compares them to the obj1 key/value pairs ? Is there a better way to do this ? or should i use a 3 loops?

the function should return the obj el in the arr that contains obj1. For example: arr[0] should be returned since it contains obj1

function objInArr(srcArr, obj) {

  var arr = [];

  //var srcLength = 0; 
  //var sourceSize = Object.keys(source).length; // The length of the source obj
  srcArr.forEach(function(el) {

    el.forEach(function(objEl){
      obj.forEach(function(sourceEl){
         if( sourceEl === objEl) { arr.push(sourceEl); }
      });
    });
  });

  return arr;
}

cнŝdk · Accepted Answer · 2017-11-19 23:10:00Z

You can use a combination of Arry#find() and Array#some() methods to loop over your array objects and find if an object with the same keys and values exists or not:

var exists = arr.find(function(o){
    return Object.keys(o).some(function(k){
          return !Object.keys(obj1).indexOf(k)>-1 || o[k]!=obj1[k];
    });
});

It will return an object if it exists, if you want to return a boolean you can change the .find() with a .some().

Here the statement !Object.keys(obj1).indexOf(k)>-1 || o[k]!=obj1[k] will quit if an object doesn't have the iterated key or it's value its' not the same.

Demo:

var arr= [{name:'John', lastName:'Smith', age:25}, {name:'Steve', lastName:'Johnson', age:56}];
var obj1 ={name:'John', lastName:'Smith'};

var exists = arr.find(function(o){
    return Object.keys(o).some(function(k){
          return !Object.keys(obj1).indexOf(k)>-1 || o[k]!=obj1[k];
    });
});

console.log(exists);

smac89 · Accepted Answer · 2017-11-20 00:21:35Z

// object contains subObject
function partialContains(object, subObject) {
    // Create arrays of property names
    const objProps = Object.getOwnPropertyNames(object);
    const subProps = Object.getOwnPropertyNames(subObject);

    if (subProps.length > objProps.length) {
        return false;
    }

    for (const subProp of subProps) {
        if (!object.hasOwnProperty(subProp)) {
            return false;
        }

        if (object[subProp] !== subObject[subProp]) {
            return false;
        }
    }

    return true;
}

You can now use it like this:

const arr= [{name:'John', lastName:'Smith', age:25}, {name:'Steve', lastName:'Johnson', age:56}];

const obj1 ={name:'John', lastName:'Smith'};

const containing = arr.find((object) => partialContains(object, obj1));

if containing is undefined, nothing was found, otherwise, the object that contains obj1 is returned.

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